Known ship propulsions have in an embodiment at least one propulsion and control unit, also indicated as rudder propellers, which is positioned underwater, and which is equipped with one or two propellers and which can be pivoted around a vertical control axis. Through the pivoting of the propulsion vector which is generated by the propeller, a steering function is achieved for the boat. The pivoting happens by means of a steering shaft which is driven by a control device.
It is known to pivot hydraulically the rudder propeller by means of a hydraulic motor. Disadvantages of a hydraulic control device are, on one hand, the large weight, the construction effort and the cost of the hydraulic components. A hydraulic pump is needed to drive the hydraulic motor which is, for itself again, driven by an electric motor or a combustion engine, which presents a disadvantage in regard to the efficiency of the entire system.
An electro motor drive of a rudder propeller is known from WO2005005249A1. Hereby, an electro motor, also named as a servomotor, drives, via a transmission which reduces the rotational speed of the electric motor, the pivoted control shaft of the rudder propeller and swivels here the directivity of the thrust of the rudder propeller around a vertical axis. Through a previous use, the design of the transmission of this electric propulsion is known as a two-step planetary transmission which is, after the electro motor, coaxial positioned to it and drives the pivoted control shaft via a following spur wheel stage. A disadvantage hereby is the respective play of the connected in series planetary gears. Also, this kind of control device requires a strong brake device to avoid an unintended torque of a pivoting propulsion unit which is created through external and internal forces. Furthermore, a control transmission which has two planetary transmission sets, positioned one after the other, has a relatively large overall length and also has a relatively large amount of parts.